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AC to DC converter with zener diode regulation Nazmus Sakib Department of EEE, Ahsanullah University of Science & Technology,Dhaka,Bangladesh. Email : [email protected] Abstract:The basic objective of the thesis is to construct a circuit that can give a constant dc 5volt. The output voltage must not have an output voltage ripple greater than one percent for its given output.The first concept to make a 5volt dc power supply is to design for a rectifier circuit to convert AC power into DC.After getting pulsating dc we have to filter it to get smooth waveshape .Then we will use zener diode to regulate the voltage and thus we will get a nearly constant 5 volt Keyword: Diode,Rectifier,Filter,Pulsating DC, Ripple voltage,Transformer,Zener diode, Regulation. A DC supply consists of the following parts: 1. A transformer to change the voltage as required and to isolate the DC circuit from the line. 2. A rectifier consisting of one or more diodes, to change AC to DC. 3. A smoothing circuit using inductors and capacitors. 4. A zener diode to regulate the voltage. 2. Equipments and Components 1.Introduction Electric energy is most often delivered in the form of alternating current . the voltage and the current alternate sinusoidally between two extremes. This cycle is repeated 50 times a second . Very often, however, and particularly for electronic circuits, direct current is desired . voltage and/or current which are stable in time. The degree of stability of the voltage varies according to how the DC is produced. A power supple converting AC to DC may, on the other hand, have a good long term stability but rather poor short term stability. In this case fast but often small variations called ripple originate from the AC input leaking through the AC to DC converter. The aim when designing a DC supply is of course to get an output voltage with good stability. Serial No. Component Details Specification Quantity 1. Transformer 220V/12V 1 piece 2. p-n junction diode 1N4007 4 piece 3. Resistor 1KΩ 1 piece 4. Capacitor 1000uf 1 piece 5. Zener diode 1N4733A 1 piece 6. Bread Board 7. Wire 1 unit as required 3.Transformation The first step is to transfer 220 volt into 12 volt to make a5 volt power supply .So we have to use a transformer to convert the voltage.. The transformer the first block of thethe converter required the ac input. A basic two pin ac plug connector was connected to the transformer allowing it to be plugged into any standard wall plug. For safety reasons we affixed the transformer in a metal case and wrapped the outside of the box in a layer of electric tape.The transformer is used for this project which is a step down control transformer.The transformer is designed to connect in series for AC-DC converter design. It is needed to input at 220 Vac, and output at 12 Vac.Here we used a center tapped & shell type transformer. The rating of this transformerInput : 220V~50Hz Output : 12V X 2 1000mA Fig1. Centre tapped transformer 4.Rectification We can convert ac signal to dc signal by using a rectifier.A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The process is known as rectification.There are two types of rectifier. 1.Half wave rectifier. 2.Full wave rectifier. Half wave rectifier:In half wave rectification of a single-phase supply, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, mean voltage is lower. Half-wave rectification requires a single diode in a single-phase supply, or three in a three-phase supply. Rectifiers yield a unidirectional but pulsating direct current; half-wave rectifiers produce far more ripple than full-wave rectifiers, and much more filtering is needed to eliminate harmonics of the AC frequency from the output. Full wave rectifier:A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to pulsating DC (direct current), and yields a higher average output voltage. Two diodes and a center tapped transformer, or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed.[3] Single semiconductor diodes, double diodes with common cathode or common anode, and four-diode bridges, are manufactured as single components. Fig3.Full wave rectifier The major disadvantages of half wave rectifier are: 1.Load recieves half of input power, 2.Average DC voltage is low, 3.Due to presence of ripple output voltage is not smooth one. The advantages of full wave rectifier: 1.wastage of power is less 2.Average DC input increase significantly. 3.Waveshape become smoother. Vripple= 11.25 1k∗50∗𝐶 10.44 Disadvantages are: 1.Require more space and bulky in use. 2.not cost effective for transformer. Or, 0.22 = 1k∗50∗𝐶 Or, C = 1000 uf. Here we use full wave rectifier for high efficiency. Vrectified (Experimental): Output voltage of transformer, Vrms= 13.4 V Peak voltage, VM =13.4* 2 V = 19.04V We know, Vrectified = 0.318*2(VM-2*Vth) Here, Vth= Threshold voltage of silicon diode=0.7V So, Vrectified = 0.318*2(17.81-2*0.7) = 11.25 V 5. Filtering: To get real dc from pulsating dc we have to filter.Actually we have to make a low pass filter because a low-pass filter is an electronic filter that passes low-frequency signals and attenuates signals with frequencies higher than the cutoff frequency.If we can reduce the value of ripple voltage we will get smooth waveshape.The most common meaning of ripple in electrical science is the small unwanted residual periodic variation of the direct current (dc) output of a power supply which has been derived from an alternating current (ac) source. This ripple is due to incomplete suppression of the alternating waveform within the power supply.In other words v ripple is the difference of maximum and minimum voltage.To reduce v ripple we can use a bigger value of capacior as the ripple voltage is inversely propotional to the value of capacitor.The equation is given below- Calculation for choosing capacitor value: We know, Vripple= Vrectified RL∗𝑓∗𝐶 Vripple= Ripple Votage 0.22 V [Assumed] Vrectified= Rectified voltage=10.44V. f= Frequency of the ripple voltage=50Hz. C= Value of the capacitor. 6. Voltage regulation: Any electrical or electronic device that maintains the voltage of a power source within acceptable limits. The voltage regulator is needed to keep voltages within the prescribed range that can be tolerated by the electrical equipment using that voltage. Voltage can be ragulated many ways such a susing IC or Zener diode .We have zener diode to regulate voltage here.As we wan to make a5 volt power supply we have used a zener diode which threshold voltage is 5 volt.So we have got 5. volt across zener diode.We havent got exact 5 volt because the zener diode voltage depends upon the resistor in series with it which is used to limit the current flow. Simulation and circuit diagram: Fig.4 : Circuit diagram. Fig 5.Simulated waveshape 7. Conclusion: The AC-DC converter design has been tested with computer simulation and analysis . It has achieved the voltage output range requirement ( 5V) . But however, the testing results also show some uncertainties about the power output of this AC-DC converter, which is below our expectation. The problem is most likely is caused by the old transformer which we obtained from the electronics shop and became inoperable after the demonstration. 8. References 1. 2. 3. Electronic Devices and Circuit Theory (Tenth Edition) by ROBERT BOYLESTEAD AND LOUIS NASHELSKY. ( Chapter1:Semiconductor diodes, Chapter 2: Diode application) Microelectronic circuits (Fifth Edition) by Sedra/Smith. ( Chapter 3: Diodes) Class lecture of Ziaur Rahman sir.